CA2109145A1

CA2109145A1 - Self-steering axle for vehicles

Info

Publication number: CA2109145A1
Application number: CA002109145A
Authority: CA
Inventors: William Goertzen
Original assignee: Individual
Current assignee: Motor Coach Industries Ltd
Priority date: 1992-10-23
Filing date: 1993-10-25
Publication date: 1994-04-24
Also published as: US5364113A; MX9306594A

Abstract

Abstract of the Disclosure A self steering axle system for motor coaches and similar commercial vehicles having a truss which hingedly supports an axle beam for pivotal movement between a normal positive caster angle and a negative caster angle when the vehicle is driven in reverse. The pivotal or rocking movement is achieved by a centrally positioned shift actuator acting through a yoke arm assembly and a latch which absorbs brake reaction forces. The system includes a caster lock for rendering the axle non-steerable in the event of a system failure or above predetermined operational speeds.

Description

`~` ~ ~ ( 1 ~10~5

2 The present invention relates to an axle assembly for commercial vehicles 4 e g motor coaches and trucks, and more particularly relates to a self-steering TAG axle which may be select*ely rocked about a transverse axis from a normal 6 positive caster angle to achieve negative caster for reverse vehicle operation.
7 Auxiliary TAG axle assemblies are commonly used to distribute loads on 8 large vehicles e.g. tractor-~ailer combinations, trucks and motor coaches.
9 These axle assemblies provide certain operational advantages but tend to turn the 10 wrong direction when the vehicle is operated in reverse. As a result, one solution 12 in the prior art is to provide a mechanism to raise the auxiliary axle during backing 13 up to avoid tire wear and scuffing.
14 Another approach in the prior art is to provide an axle system which is self 1~ steering aDd which allows the wheels to turn to the right or left without mechanical 16 connection to the steering gear. For example, U. S. Patent No. 4,770,430 discloses 18 a self-steering axle assembly in which the longitudinal axis of the king piD
19 assemblies ale inclined at different angles for forward and reverse vehicle 20 movement~ The steering axle assembly of this patent has a transYerse a~e 21 supportable on the vehicle frame with a l~ng pin assembly mounted on the outer 23 end of the axle with a wheel mounted on the king pin assemblies for rotation about a transverse axis. The wheels are interconnected so that they steer together 24 through a tie rod. The axle mcludes a pivot affording pivotal rnovement of the 26 king pin assemblies relative to the vehicle frame between a forward position and l ~ -~1~91~5 1 a reverse position. The king pins are selectively moved between the forward 2 position for forward movement of the vehicle and the reverse position for backing so the wheels properly track in both directions.
4 U.S. Patent No. 4,120,509 discloses a pair of transversely extending wheel 6 axles which are slidingly and pivotally attached to a pair of long~tudinally extending 7 walking beams for the angular variation of the two-wheel a7~is during vehicle 8 turning and independent movement of each a~e out of the plane common to the 9 two axles. A transversely extending steering unit pivotally attached to the walking 10 beam between the two axles transfers the load of the vehicle to the walking beams.

12 As the vehicle executes the turn, the steering unit rotates in the direction of the 13 turn while the walking beams tend to maintain a straight-drive orientation. The 14 rotation of the steering unit is transmitted to the front axle by a pair of steering 15 arrns causing the front axle to rotate relative to the rear axle in the direction of the 16 vehicle turn.
17 U.S. Patent No. 3,334,912 discloses a vehicle wheel support for trailers 18 having an adjustably positioned wheel assembly. Each of the sets of wheels is mounted vertically pivotal about a generally longitudinally extending axis as well 21 as vertically pivotal about a generally laterally extending axis. The vehicle support 22 construction provides independent pivoting of each individual set of wheels to 23 compensate for uneven surfaces in a lateral direction, independent pivoting of each 24 individual set of wheels to compensate for uneven roads in a longitudinal direction.
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1 U.S. Patent ~o. 4,831,747 shows a suspension system incorporating upper 2 and lower torque rods pivotally connected between a hanger and an axle. The upper torque rod is a hydraulic cylinder piston assembly. In the extended 5 condition, the upper torque rod pivots the axle to a forward pitch in which it is self 6 steering when the vehicle is driven forward. In the retracted condition, the upper 7 torque rod pivots the axle to a negative pitch condition in which it is self steering 8 when the axle is operated in a reverse direction. The hydraulic cylinder is actuable 9 by the driver when the gears are shifted between forward and reverse. The 10 hydraulic cylinder may be operable in response to operation of the vehicle gear 11 shift lever.

13 U.S. Patent No. 2,415,460, discloses a structure for motor vehicles such as 14 buses having a pivoted truclc having steerable wheels in which the steerable wheels 15 are automatically acljusted by relative movement between the truck member and 16 the superposed portion of the body.
17 Other patents of interest in the art are as follows:
18 Patent No. Patentee Title ~9 2,847,228 J.E. Hall Wheel Suspensio~ For Trailers 21 3,704,896 W. H. Buelow et al Au~liary Steerable Wheels For Vehicles 22 3,880,440 H. Tidewell Steerable Truck With Reversible Castering 23 Wheel Structure For Trailers ~`
24 4,084,833 W J. Mohrbacker Castered Load TraIIsfer Axle Stabilizer ~ ~ 4,19S,856 T. Larsor~ et al High LiftTag ~de Load Tramsfer System 28 ~:

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1 4,373,738 D. M. Lange Steerable Au~liary Wheel Assembly For 2 Vehicles

3 ~,449,727 B. Roos Skid Control Car

4 5,015,004 J. L. Mitchell Elevating, Reversible Self-Steering Suspension System 7 5,01~,756 J. L. Mitchell Control For Self Steering Suspension Assemb]y 8 Accordingly, it is a primary object of the present invention to provide a self-9 steering a~e assembly for vehicles e . g . motor coaches which assembly will reduce turning radius, reduce tire scufEing and scrubbing, minimize steering effort 11 and generally irnprove overall vehicle maneuverability and stability.
12 Briefly, the present invention provides a self-steering TAG axle for vehic]es 13 which utilizes a standard steering axle similar to the conventional front axle of a 15 motor coach which has'wheel assemblies at either end of the axle. The a~e system 16 has a truss which is positioned above the steering axle to provide a platform to 17 support air spring bellows at either end. The truss also provides attachment 18 locations ~or the upper and lower radius rods. The truss is hinged to the a~e at 19 maintenance-free, resilient or sirnilar bushings to allow predetermined pivotal or 21 rocking movement of the axle while restrained by the upper a~d lower radius rods.
22 The rocking movement is controlled by a centrally positioned shift actuator acting 23 on a yoke aIm through a latch mechanism at the upper end of the arm. The 24 actuator movement produces a change between posit*e and negative caster angles 25 for self s~eering in both forward'and backward vehicle travel directions. To ensure 26 that' brake reaction and road input forces are Icept out of the caster actuation 21U9~
. 1 circuit, the mechanical latch mechanism provided at the upper end of the arrn 23 absorbs brake reaction forces bypassing the actuator. The system is completed by 4 a tie rod lock mechanism which provides an override to render the axle noll-

5 steerable in the event of a system failure. The tie rod lock consists of an actuator

6 having a piston with a lock pin which is extended when the system fails to lock the

7 tie rod e~ending be~veen the wheels. An adaptation of the tie rod lock

8 mechanism may be used as an alternative to the afore-mentioned mechanical latch

9 mechanism for caster change locking purposes. The activation of the tie rod loclc 11 and shift operations may be accomplished by various control devices which sense 12 operational conditions, either electrical or mechanical. A speed switch can be set 13 to energize the tie rod lock in the locked position above a predetermined speed for 14 stability. The locking function may be achieved at anytime by a manually operable 15 override switch.

18 In the accompanying drawings: ~ :
19 ' .
Figllre 1 is a perspective vicw oE the selE steering axle o~ the present 21 invention with the opposed wheel assemblies sho~,vn in dotted lines;
22 Figure 2 is an enlarged, side elevational view of the axle assembly shown in 23 a forward operating position with the shift control circuit shown schernatically;
24 ~ ~;
Figure 3 is an enlarged, side elevational view of the axle assembly shown in 26 a reverse operating position with the shift control circuit shown schematically;

'~ ' ~ 21031~5 1 Figure 4 is an elevational view of the self steering axle taken from the rear 32 f the axle;
4 Figure S is a side elevational view of the latching mechanism in the normal 5 latched forward position;

6 Figure SA is a side elevational view of the latching mechanism in the 7 unlatched forward position;
8 Figure SB is a side elevational view of the latching mechanism in the back-9 up position;

11 Figure 6 is a detail view partly in schematic of the tie rod loclc as i~dicated 12 in Figure 2 in a locked position;
13 Figure 6A is a detail view partly in schematic of the tie rod loclc in an 14 unlocked position;
1~ Figure 7 is a side elevational view of a motor coach embodying the self 16 steering axle shown in the normal forward direction of vehicle travel;

18 Figure 8 illustrates the underside of a motor coach chassis equipped with 19 a self-steering axle with the wheels shown in a forward left turn position as 20 indicated by the arrow;
21 Figure 8A illustrates the underside of a motor coach chassis equipped with 22 a self steeling axle with the wheels shown in a backing right turn position as 24 indicated by the arrow; .
Figure 9 is a representative schematic diagram of the electrical and .
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226 pneuma~c systems for the caster latch;

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1 Figure 10 is a representative schematic diagram of the tie rod lock system;
2 and Figure 11 is a top view of the latch shown in Figure 5.
The self-steering axle system of the present invention is generally designated 6 by the numeral 10 and is of the type which is operatively secured to a vehicle such 7 as a bus or motor coach 11 behind the fixed drive wheels 15, as shown in Figure 8 7. Nolmally the vehicle engine of a motor coach is located rearward of the rear 9 wheels and the drive shaft extends forward to drive wheels 15.

11 As seen in Figure 4, the vehicle 11 has a chassis with frame members 14 to 12 which the self steering axle assembly 10 is attached at spring mernbers shown as 13 aiT bellows 30, 32 interposed between the axle and ~ame. The axle assembly has 14 a superstructure in the form of a suspension truss generally designated by the 15 numeral 16 having transversely-extending structural members 18 and 20 which at 16 their inner ends are connected to a junction box 22 centrally located on the 17 lo~gitudinal centerline 25 of the vehicle. The junction box and truss are 18 syr~imetrical with respect to centerline 25. ~e outes end of the horizontal truss 20 members 18 and 20 support pads 24 and 26 located on the upper ~surface of the 21 truss members. Air spring or air bellows assemblies 30 and 32 are interposed 22 between the ends of the honzontal truss members and the vehicle chassis. The air 23 springs have a resilient, bladder-like housing and are connected to a source of 24 compressed air for selectively inflatin" and deflating the air springs through a 1~ ' .
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1 suitable control arrangement to control the ride of the vehicle, as is well known in 2 the art.
4 The description herein is with reference to a parallel arm suspension system ~ but it is to be understood that the axle arrangement may be used with other ~pes 6 of suspensions e . g . trailing arm and leaf spring systems which are well-known.
7 With such systems, the suspension member would be directly attached to the truss 8 or beam and the truss or beam would embody the hinge element to provide the 9 axle rocking motion.
The left side of the suspension truss arrangement as viewed in Figure 4 has 11.
12 a pair of downwardly converging structural members 34 and 36 which are 13 connected at their lower end by welding. A reinforcing side plate 38 may be 1~ prov~ded at the intersection of the structural members 34, 36. The members 18, 15 34 and 36 are arranged in a general triangular configuration establishing a portion 16 of a s:ructural truss.

18 The right hand portion of the suspension truss is similarly configured having 19 members 34A and 36A joined at their lower ends and reinforced by plate 38A
forming another triangular configured truss section. A retainer plate 40 is welded 21 to the outer surface of truss member 34. Similarly, a plate 42 is welded to the side 22 of truss member 36. Plates 40 and 42 each define an aperture or bore 44 which 23 receive an extending portion of axle hinge connection, as will be explained. Plates 24 40A and 42A are similarly positioned at the lower ends of ~uss members 34A and 26 36A and receive the right hand axle hinge connection. The transversely extending ^` i 2103~
1 transverse centerline of the axle hinge cormections are indicated by the numerals 2 S0 and 50A.
4An upper radius rod 52 has its inner end 54 retainably received within 5 section 56 of the upper radius rod junction box 20. The opposite end of the upper 6 radius rod 52 is pivotally secured to ~ame member 60 at connection 62 in 7conventional manner. Radius rod 52A extends in similar marmer having its inner 8end 54A received in the section 56A of the upper radius rod junction box. The 9outer end of the radius rod 52A is connected to fixed frame member 60 at 10connection 62A. The radius rods are provided with conventional torsional rubber 12bushings and are of fixed length. The upper radius rods along with the lower 13radius rods, as will be explained in detail hereafter, establish a fixed length 14suspension system.
15The axle portion of the assembly is generally designated by the numeral 80 16and is hillged to the truss and includes a generally horizontally extending intermediate beam section 82 having opposite ends 84 and 84A. The intermediate 1~ .
19 beam section 82 may be solid or may be in the forrn of a box-like structural 20 member as indicated and may be a standard front steering a~le. The ends 84 and 21 84A are vertically offset ~om section 82 and each defines a generally vertically 22 extending bore 88, 88A which bores are adapted to receive the l~ng pin of the 24 associated wheel assembly 85.
The steering assembly includes a king pin assembly which is pivotal about 26 the a~es 90 a~d 90A at each wheel 85. As indicated, the axle may be a standard 28 .

; 2~9~ ~5 1 front steering axle and wheel assembly with drums or discs and brakes, not shown.
2 The conventional steering arm or steering mechanism is not required and is 4 omitted. As best seen in Figures 2 and 3, a tie rod 96 extends transversely between 5 the wheels 85 and is located forward or to the rear of the axle assembly. The 6 pivotal connections between the ends of the tie rod 96 and the wheels are 7 conventional and further description is not deemed necessary. As seen in Fignre 8 3, the kingpin angle ~caster) is shown as -3 from the vertical plane.
9 Ille axle 80 is mounted so that it may be rocked or pivoted about hinge

10 connections 10S, 105A from a predetermined normal positive caster angle to a

11 negative caster angle. For example, in the normal for~,vard travel mode, a posit*e 13 caster angle of approximately 3 is maintained. When the vehicle is placed in 14 reverse, a rocking action occurs in the hinge connections to produce a change in 15 caster from the normal built-in positive angle to a negative angle, for example -3 16 which is sufficient to yield effective caster action when the wheels rotate in the 18 reverse direction. Connections 105 and 105A are rubber bushed and are 19 positioned at spaced-apart locations attached to the upper surface of the a~le beam 20 82 and are connected to the lower ends of the triangular truss sections.
21 A first box-like receptacle 110 is positioned below the hinge assembly 105 22 on the underside of the left-hand section of the axle. A similar box-like receptacle 23 110A is positioned on the underside of the right-hand section of the axle below the 224 hinge assembly 105A. Radius rod 112 has one end 114 secured in receptacle 110 26 by transversely extending pin 116. The opposite end of lower radius rod 112 is : ~
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secured to the lower end of frame member 60 by transversely extending pin 3 connection 61. The opposite lower radius rod 112A extends in similar fashion 4 between frame member 60 and box 110A~. The upper and lower radius rods 5 establish the geometry of ~he suspension system and assume the respective 6 positions in forward and reverse travel as seen in Figures 2 and 3.
7Caster angle control of the a~cle beam 80 is imparted through a yoke arm ~ assembly 125. The yoke arm is centrally positioned on the axle member 82 and has 9 a general U-shaped mounting bracket 128 at its lower end which is centrally 11 attached to the upper surface of the axle. A pair of upwardly extending arrns 129 and 129A are attached to the ends of the U-shaped mounting bracket 128. The

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13 arms 129 and 129A extend forwardly and angle slightly inwardly toward the vehicle 14centerline 25. The upper end of arms 129 and 129A are joined to a centrally 15 positioned latch arm 135. The latch ann 135 is secured to the arms by cross-16 member 138 extending between the upper end of arms 129 and 129A. The latch 18 arm 135 is part of a latching mechanism 180 that controls the caster angle shift 19 cycle. The latching mechanism will be described in detail hereafter. The yoke arm 20 assembly 125 permits the drive shaft 134 to pass through the yoke arm at a 21 longitudinally central position with respect to the vehicle. The yoke arm serves as 22 a containment housing in the event of drive shaft breakage.
23In the normal forward operatmg position, the self steering axle assembly is 24 in the position shown in Figure 2 having a predetermined positive caster angle as 26~ ~ for examplc 3. he center of the spnndle is jD the position indicated by the ~8 ~ .

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1 numeral 160 and the centerline of the king pin in the forward position is indicated by line 90. When the axle assembly Is rocked about the lateral axis through the 4hinge connections 105 and 105A, a caster angle change is imparted from the 5 normal positive caster angle to a negative caster angle as for exarnple a negative 6 3. In the negative caster angle position shown in Figure 3, the spindle center 7 assumes the position indicated by the numeral 160 and the axis of the king pin has 8 shifted to the position indicated by the numeral 90.
Simultaneous activation of the caster change for both wheels is 10 accomplished by a force applied from a single power source to the upper end of 12 the actuator yoke arm 125. The actuation force is shown applied by an act~ator 13 such as an air cylinder 175 centrally mounted on the top of the superstructure at

14 bracket 176. A resilient bushing 179 is interposed between the bracket and the

15 latch. It ~ill be obvious that a hydraulic system could also be utilized. The

16 cylinder has an extensible rod 252 which applies an actuating force to the yoke and 18 axle through latch mechanisrn 180 as will be explained. The force generated by the 19 cylinder 17j is required only to overcome the caster shift resistance. Brake 20 reaction forces are not imposed in the caster shift actuation system when the 21 vehicle is at rest or in forward motion. In reverse, braking forces in the actuation 22 circuit are of low order of magnitude and can be absorbed by the cylinder.
23To insure that brake reaction forces are elirninated ~om the caster shift 24 actuation circuit in the forward motion mode, latch mechanism 180 is incorporated 26 which absorbs brake reaction forces, bypassing the actuating c~linder. In the event ~ ~ 21091~i 1 of a system failure, the latch mechanism 180 also maintains the structural integrity 2 of the axle for brake reactions. Without the latch feature, braking loads and shock 4 loads would have to be absorbed by the cylinder 175. These loads are considerably 5 higher than those required to achieve the shift cycle alone. Further, loss of 6 cylinder pressure would allow an uncommanded shift to the back-up mode to 7 occur.
8The latch mechanism 180 is best seen in Figures S, SA, 5B and 11 and 9 consists of a clevis 190 having a generally U-shaped configuration with horizontal 11top 1g1 and opposite side walls 197 and 194. The clevis extends axially and is 12 secured to the end of cylinder rod 252. The upper end of the latch ann 135 has 13 an upwardly projecting tab 195 which extends between the side walls 192 and 194 14 of the c]evis. A thrust bar 200 extends transversely between the side walls of the 15 clevis spaced inwardly from the distal end of the clevis. The outer end of the clevis 16 carries a roller 202 secured on axle 204 extending transversely between the walls

17 of the clevis. Rollers 205 and 205A are provided on opposite sides of the latch

18

19 arm 135 and engage the bottom edge of the clevis side walls.
20A latch tongue 210 straddles clevis 190 and is secured to truss bracket 176, 21 through loosely fitting holes by a pair of bolts 178 located on opposite sides of 22 cylinder 175. The latch tongue ~10 is biased downwardly by a pair oP annular 23 elastomeric bushings 179 located on the attachment bolts. The bushings are 24 compressed between the latch tongue 210 and the bracket 176. A greater 26 compressive force is applied to the upper side of the bushings to yield the required ~27 13 21091~5 1 downward bias for the appropriate latching action. Differential adjustment of the 2 bolts provides az~muth adjustment for optimum alignment of the tongue apertures 4 215 and 220 with the tab 195 of the latch arrn 135. Mechanical springs arranged 5 in conventional manner may be used to provide bias in lieu of bushings 179.

6The tongue defines two axially spaced-apart apertures 215 and 220.
7Aperture 220 is located near the distal end of the latch tongue and aperture 215 8 is spaced inwardly. In the normal latched position, tab 195 at the upper end of the 9 latch arm post engages aperture 215 as shown in Figure S. In the back-up position, 10 tab 195 on the end of the latch arm post is engageable in aperture 220 as seen in 12 Figure SB.
13The clevis 190 traps the latch arm 135 translating linear motion of the 14 piston rod 178 to rotational motion of the axle. Thrust forces are exerted by the 15 thrust bar 200 and retraction forces are exerted through the roller axis pin on the 17 end of the clevis.
18A cam 230 depends from the latch tongue having inclined cam surfaces 232 19 and 234 at opposite ends. These cam surface translate the hori~ontal linear motion 2~ of the cylinder to rotational motion of the tongue upwardly to release the actuating 21 arm. The rollers 202 on the clevis support the tongue at the correct position and 22 reduce surface friction throughout its travel range. Rollers 205,2û5A on the arm 23 135 support the clevis preventing bending loads from reaching the cylinder ram or plston. .

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1 The operational sequence of the latch mechanism is as follows: The latch 2 mechanism is in a normal position as shown in Figures 2 aDd 5 prior to receipt of any input signals. The operating system is shown as a pneumatic system, although 6 it may also be hydraulic and is described hereafter with respect to Figure 9.
6 Solenoid valve 250 is positioned so that supply air is directed to the rod end 252 7 of cylinder 175 and the cylinder head end 254 is connected to exhaust. The 8 actuator 175 is fully retracted so that the clevis is retracted trapping tab 195 and seculing the arm 135 against the truss 16, as seen in Figure 5. In this position, the 1l axle has a predetermined positive caster angle, as seen in Figure 2. The thrust bar 12 200 is spaced from the upper tab 195 on the actuating arm post.
13 As indicated by Figure 9, shifting the vehicle into reverse gear ~Yill cause 14 either a mechanical sensor or elec~rical sensor in the back-up light circuit to open 15 valve 250 exhausting air or hydraulic pressure ~om the rod end 252 of the cylinder 16 175.

18 Solenoid valve 250 is operatively connected to the shift cylinder 175 as 19 shown in Figures 2 and 3. The system is shown in Figure 9 and operates from the

20 baclc-up light switch 260 which, when energized, energizes relay 262 and associated

21 contact 262A. Valve 250 has a spring return so that at start-up, the a~e is in the

22 forward mode, Figure 2. Panel indicator light 268 is out. When the operator

23 selects reverse gear, relay 262 is energized closing contact 262A causing the shift

24 panel light 268 to illuminate and enere,~zing valve 250 directing air to the head end ~ 9 ~ 1 ~
1 ~5~ of the cylinder. Reed switch 270A senses the end of the shift cylinder travel 2 and energizes relay 264 opening contacts 264A extinguishing the panel light ~68.
4When the operator shifts out of reverse, the panel light illuminates and air 5valve 250 under the influence of the spring return, directs air to the rod end 252 6 of the cylinder. Reed switch 270 senses the limit of the cylinder travel and ~ ex~inguishes the light 268. In the event a power failure occurs, the system will shift 8 to the forward travel position shown in Figure 2.
9In the reverse mode, the head end 254 of the cylinder is pressurized to 10extend the piston and rod 178. I~e rod and clevis extend and the clevis roller 202 12 contacting the cam 230 on the tongue forcing the tongue upwardly against the 13 spnng pressure exerted by members 179, disengaging the latch arm post from the 14 latch tongue, as seen in Figure SA. Further extension of the cylinder piston will 15 cause the thrust bar 200 to engage the latch arm post forcing the latch arm post 17 outwardly with the thrust bar.
When the cylinder travel approaches the end of its strolce, as seen in Figure 19 SB, the clevis rollers are clear of the tongue cam allowing the tongue to drop down 20 trapping the actuating arm post ~n the second aperture 2~0 located near the distal 21 end of the latch tongue. The a~e assembly has now assumed the negative caster 22 an~le position shown in Figure 3. C~,rlinder 178 is maintained in the extended 23 position until the operator makes a gear shift change out of reverse causing the 24 axle to return to the forward position of Figure 2 as described above.

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1The functional sequence of events from baclc-up mode to the norrnal mode 2 is essentially the revelse of that described above and therefore detailed description 3 is not necessary.
5To complete the system, a tie-rod loclc mechanism provides a number of 6 operational advantages, including the provision of an override feature to render the 7 vehicle operable as a non-steerable axle in the event a system failure results in the 8 axle being stuck in an undesirable caster position. The tie-rod lock also restores skid control effective at vehicle highway speeds. I'he tie-rod lock mechanism is10 best seen in Figures 2, 3, 6 and 6A and is associated with the transversely 12 extending tie rod 96. The tie-rod lock includes a loc}c cylinder 270 which is 13 mounted on bracket 272 extending outwardly from the axle beam. A lower plate 14276 also extends from the axle defining a space with bracket 272. A pair of aligned 15apertures 278 and 280 are provided in plates 272 and 276, respectively. Plate 282 16 is slidable between plates 252 and 256. An aperture 284 is provided in plate 282 17and aligns with apertures 278 and 280. Cylinder 270 is provided with a loclc pin 19 286 secured to the piston rod. The pin 286 is aligned with the three apertures and 20 normally the lock pin is held in the extended position of Figure 6 by spring 285 21 interposed between the body of the cylinder and retaining washer 287 which 22 extends annularly about the pin. In the extended position, the pin engages the 23 apertures in all three plates locking the tie rod 96 which is secured by a clamp 290

25 at bolts 292 at the outer end of the interrnediate plate 262. This arrangement

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21U~l~SI

1 locks the tie rod, the latter being in double shear eliminating bending stress being 2 imposed on the lock pin and cylinder rod.
The tie rod lock cylinder 270 is pressurized across solenoid-operated valve 4 300 when the system is operated causing the loclc pin 286 to be retracted from the 6 apertures freeing the tie rod 96 for self-castering.
7 Figure 10 is a schematic diagram of the tie rod lock actuator system. When 8 main power source is off, the spring return on the solenoid valve 300 ensures that 9 the tie rod is locked. Figure 10 is a simplified electrical diagram of the tie rod lock 11 circuit with the power "ofE'.
12 When power is "on", valve 300 is energized to direct air to retract the lock 13 pin 286 to the position shown in Figure 6A. The panel warning light 310 remains I4 off and the tie rod is unlocked. At a predetermined speed, speed switch 302 de-15 energizes the valve 300 and the tie rod is locked. Below the predetermined speed, 17 the speed switch 302 will re-energize the air valve 300 to unlock the tie rod.
18 The override switch 320 permits the operator to manually cut off power to 19 lock the tie rod. The reed switches 312 and 312,A sense the position of the locl~ng 20 cylinder illuminating the panel warning light if abnormalities occur.
21 From the foregoing it will be appreciated that the self steering axle of the 22 present invention provides the follow~ng advantages:

24 1. The axle system utilizes a standard front steering axle with tie rod, 2~ drums, bralces and wheels but without steering arm and/or steering mechanism.

27 18

28 ~: 2 1 ~ 3 ~ 4 5 1 2. A superstructure or truss is provided which provides a support for air 2 bellows and suspension elements or other spring damper devices.
4 3. The hinge connections are transversely located on the bottom of the 5 truss or superstructure to provide hinge points for the axle assembly. Rocking or 6 pivoting OCCUIS about a lateral a~s to produce a change in caster from the normal, 7 posit*e angle through 0 to a negative angle sufflcient to yield effective caster 8 action when the vehicle is operated in reverse.
9 4. Simultaneous activation of ciaster change for both wheels is achieved by 10 actuation force applied from a single centrally positioned source.
11 5. The connecting member between the shift force application point and ~2 13 the axle serves as a containment yoke for the drive shaft in the event of drive shaft 14 bleakage.
6. The position of the system components optimi~es mass and force 16 requirements for effective conservation of weight and operating energy demands.
17 7. The forces generated by the power source (air or hydraulic cylinder) are 19 required to overcome caster shift resistance only. Brake reaction forces do not enter the caster shift actuation circuit when the vehicle is at rest or in forward 21 motion. In reverse, braking forces in the actuation circuit are lower and can be 22 absorbed by the cylinder.
23 8. To ensure that brake reaction forces aTe kept out of the caster shift 24 actuabon circuit in the forward motion mode, a supplementary mechanical latch26 ` 210~
1 mechanism is incorporated. This mechanism absorbs brake reaction forces by-2 passing the actuating cylinder/circuit.
4 9. Timing of latching and unlatching functions of the mechanism is 5 dependent on cylinder sensing rnovement.

6 10. Latching and unlatching functions are achieved by utilizing a portion7 of $he actuating cylinder stroke.
~ 11. In the event of a system failure (electrical/pneumatic/hydraulic) The 9 latch mechanism ensures that structural integrity for brake reactions is 11~ mechanically maintained.

12. The axle hinge joint geometry allows the use of fixed-length suspension 13 members ~hroughout. With fixed-length suspension members, the geometric 14 integrity of the system is optimized, i.e. in for~vard vehicle motion the suspension 15 system and air bellows funcbons are unaffected by the design. With the vehic]e in 16 reverse, no deviant displacement of air bellows is caused by the design throughout 17 its range of travel. A negligible tilt angle only is introduced to the base of the air 1~
19 bellows in this mode.
13. Signals for automatic activation of the caster shift cycle through a 21 variety of known control devices (hydraulic/electricaVpneumatic/solenoid valving, 22 etc.) are available from various sources on the vehicle, e.g. back-up light, baclc-up 23 light switches, back-up controls or levers, etc.
24 14. A tie-rod lock mechanism is included to provide an override feature to render the vehicle operable as a no~-steerable axle in the event that a system 27 20 ~
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1 failure results in the axle being stuck in the "reverse" mode and to restore skid 23 control effectiveness to the vehicle at highway speeds.
4 15. The tie rod loclc cylinder is activated when the master switch is on and 5 causes the lock pin to be retracted freeing the tie rod for self-castering.

6 16. A speed switch controlled from the speedometer can be set within the 7 desired speed range to energize the tie rod lock cylinder to the "lock" mode above 8 the set speed.
9 17. In the event of an air or electrical system failure, a spring load feat~re 10 on the cylinder pin ensures that the tie rod is loclced.

18. Indicator lights on the instrument panel are illuminated whenever a 13 "lock" or "latch" abnormality occurs. The visual warning system may be augmented 14 by an audible warning system.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A self steering axle assembly for a vehicle having a frame and a back-up system for effecting a caster angle change from positive to negative upon the vehicle being shifted from forward travel to reverse travel, said axle comprising:
(a) a suspension truss member extending transversely of the vehicle and being secured thereto;
(b) an axle beam extending transversely of said vehicle and being hinged to said truss for rocking movement relative thereto between a positive and a negative caster angle, said axle having opposite ends for receiving a king pin assembly and associated wheel assemblies;
(c) arm means extending from said axle beam at a central location; and (d) actuator means operably connected to said arm means at connector means for selectively rocking said axle to effect a predetermined change of caster angle.

2. The axle of Claim 1 wherein said arm means comprises a centrally positioned yoke.

3. The axle of Claim 1 further including spring means interposed between said truss member and said frame and fixed length suspension members extending between said axle and truss and said frame.

4. The axle of Claim 3 wherein said spring means comprises at least one inflatable bellows and said suspension member comprises an upper pair and a lower pair of radius rods.

5. The axle of Claim 1 further including a control system response to vehicle travel direction to selectively actuate said caster change actuator.

6. The axle of Claim 5 wherein said control system is operatively responsive to energization of the vehicle back-up indicator system.

7. The axle of Claim 1 wherein said actuator is an air cylinder centrally positioned along said axle.

8. The axle of Claim 1 further including a tie rod extending between the vehicle wheel assemblies.

9. The axle of Claim 8 including locking means for selectively locking said tie rod and a control system for selectively actuating said locking means.

10. The axle of Claim 9 wherein said locking means includes a clamp disposed about said tie rod secured to a slidable locking plate defining an aperture and fixed actuator means having a locking member normally out of registry with said aperture and selectively operable to move into registry with said aperture to lock said tie rod.

11. The axle of Claim 1 further including a latch member interposed between said actuator and said arm means, said latch member having means to absorb brake reaction forces when the vehicle is traveling in a forward direction.

12. The axle of Claim 11 wherein said latch includes a latch tongue secured to the frame defining a first positive caster angle position and a second negative caster angle position, said first position placing said arms adjacent said truss.

13. The axle of Claim 12 further including camming means operative to disengage said latch member during shifting.

14. The axle of Claim 9 further including an override to selectively render the axle non-steerable in the event of a control system failure.

15. The axle of Claim 9 wherein said control system includes speed sensing means which is operable to activate said tie rod locking means above a predetermined speed.

16. The axle of Claim 12 including adjustable biasing member interposed between said tongue and said frame permitting the relative position of said tongue and arm means to be adjusted.

17. A vehicle having a frame supported on an axle and wheels and being operable in forward and reverse directions of travel and having a control system indicating travel direction, said vehicle including:
(a) a superstructure extending transversely of the vehicle adjacent said axle having wheels and fixed length suspension members attached thereto;
(b) an axle beam extending transversely of said vehicle generally subjacent said superstructure and being hingedly connected thereto for pivotal movement between a normal positive caster angle for forward travel and a negative caster angle for reverse travel, said axle beam having wheel assembles at opposite ends thereof and a tie rod extending therebetween;
(c) shift arm means extending at an intermediate location along said axle beam;
(d) power means for selectively moving said shift arm to effect a caster angle change;
(e) latch means associated with said shift arm having means to absorb reaction forces in forward travel; and (f) locking means for selectively locking said tie rod to render said axle operable as a non-steering axle.

18. The vehicle of Claim 17 wherein said superstructure comprises a truss.

19. The vehicle of Claim 17 wherein said actuator comprises a pneumatic cylinder and said power means is responsive to said control system to effect a change in caster angle.